The funny part is that they actually did (Ed Visteurs was one of them). I recall reading some article where one of the actors said, "shouldn't you be able to see our breath if we are trapped in a crevasse at 8000 meters?", to which the director responded, good question, lets ask the consultants. The consultants responded that yes you would see your breath, additionally, you would be coughing, having a hard time speaking, etc. The director responded that it didn't look good in the film so they wouldn't be doing any of that.
Now if you want to see a film that is worse that Vertical Limit, watch "Take it to the Limit"